Spin‐Orbit Misalignment in Close Binaries with Two Compact Objects

Abstract

Spin-orbit misalignment in coalescing compact binaries a†ects their gravitational radiation waveforms. When the misalignment angles are large (Z30¡), the detection efficiency of the coalescence events can decrease signiÐcantly if the misalignment e†ects are not modeled. In this paper, we consider the forma- tion of close compact binaries and calculate the expected misalignment angles after the second core col- lapse event. Depending on the progenitor parameters and the assumptions made about supernova kicks, we Ðnd that 30%È80% of binaries containing a black hole and a neutron star that coalesce within 1010 yr have misalignment angles larger than 30¡, and a signiÐcant fraction of them could remain undetected. The calculations allow us to place strong constraints on the progenitors of such binaries and the kick magnitudes required for their formation. We also discuss the formation of close binaries with two black holes and the e†ect of nonisotropic kicks.